Ampeg Gemini G-15 service questions

[mattattnet]

Hi,

I just got an Ampeg G-15 with 7591 output tubes, that looks to need a cap job and some minor repairs. Have done this work on other amps, but this one has a double throw switch with positive and negative polarity settings. Is it best to go to a 3-prong grounded power cord, and convert to a standard 2-position standby switch?

Thanks,

Matt

[Snapcase]

Sure, 60's safety regulations were not exactly safe. Better go for 3-prong.

[slowhand401]

Matt, Unless you are absolutely positive about the wiring (polarities) of all the places you use your amp, I would leave the two prong cord, and DPDT
(center off) switch in place. The center "off" position is "standby" and the other two positions will reverse the polarity if you have excessive hum or you're getting shocked. You could go to a 3 prong cord and wire it like the 2 prong cord (white to white and black to black with the green going to the chassis as a ground). That will give you an added level of protection as far as getting "shocked" but only to the degree of all the other elements that are involved. ie; water, other amps polarity etc. etc. etc..... Long story short,
change the cord if that makes you feel more comfortable, but DO NOT change
the DPDT switch......! Randy

[J Martin]

You should always have a grounded cord on your amp. Make sure the hot wire (black) goes first to the fuse then to the switch, with the neutral wire going directly to one side of the transformer primary. Wire the three position switch so that both positions only switch the hot wire. There is no need to switch "polarity" with a grounded cord. The proper way to connect the ground is to have a separate screw in the chassis with nothing else connected to it except the green wire from the line cord. Use a lug that has teeth like a lock washer. I keep #10, #8, and #6 lugs on hand in my shop. You can also dispose of the old capacitor they used on one side of the two conductor line cord. although, if it shorts, the grounded cord will keep the chassis from becoming "hot".

[slowhand401]

Martin, ALWAYS, is a pretty strong statement....! That's somewhat akin to,
never, say never.... If that is the case, why is it that I have so many amps with only a two prong cord and I am still alive....? (40 + yrs)(and the 40 + yrs before that...) I stand by my earlier statement - if one feels the need for a grounded chassis - then by all means, do THAT. However, a grounded chassis does not eliminate the possibility that you will have a situation of "reverse" polarity, when compared
with all the other possibiities - of other amps, P.A.'s, and wall plugs not properly wired in the first place.... My responce was to a question about an Ampeg Gemini II. Leave the DPDT (center off) switch in place, and add a 3
prong cord if that makes you feel more comfortable. But adding that green wire to the chassis will in no way eliminate the possibitiy of having a situation of "reverse" polarity.
Having a grounded chassis might keep you from being electrocuted if you are playing in the rain, but only if all of the wall rectibles are wired to ground, which is not always (seldom is... ) the case..... With all due respect....Randy

[Enzo]

What do you mean by "reverse polarity?"

If the wall outlet is wired wrong, I suppose they could have the hot running to the third prong, and then the chassis would be hot. Unfortunately that leaves ground and neutral for the two power prongs. In that case no two wire device will power up at all, nor will a three wire. If ground and neutral are reversed, then the gear will probably function, but will be noisy - two or three wire.

There are people who smoke three packs a day, those who drive home drunk every night, who do crack at work or while pregnant. And they get away with it. Doesn't mean it is safe or free of risk, it just means they got away with it.

There are miswired outlets to be sure, but to say they seldom are wired right is silly.

If your chassis is grounded, and the amp next to yours is not, and THAT amp gets a hot chassis, then Yes you can get a poke touching both. HAving your amp grounded though prevents IT from being a cause of such situations.


I can think of no reason NOT to make an amp three wired.

[slowhand401]

Enzo, If you don't know what "reverse" polarity is, then I don't see what you can add to this conversation... (one way or the other)....(have some more
cool-aid...)

[Mark Black]

slowhand401, Junior Member, Join Date: Jul 2007, Posts: 4

vs

Enzo, Senior Member, Join Date: May 2006, Posts: 1,568

mattattnet - listen to Enzo, J Martin, and Snapcase - do the three-wire cord conversion PROPERLY including removal of the "death cap" and wiring to modern conventions of hot-fuse-switch.

Additionally get an AC outlet tester from Radio Shack or the like and USE IT before plugging your amp in. If it shows a mis-wire find another outlet and let the venue know they have a potentially deadly & wallet-draining-lawsuit problem on their hands.

There are reasons why modern electrical codes exist and a lot of them probably have at least something to do with somebody dying or getting sued.

[Enzo]

Slow, you appear to be new here, and I welcome you. I am not sure why the hostility must be included with some simple disagreement, if that is what we are having. We usually try not to make things into fights here.

I understand reverse polarity certainly, but am not sure exactly what you refer to when you use the term here. Reversed wires in the wall outlet? Reversed wires in some other gear? I am not being a smart ass, I genuinely want to know what you are considering. If there is a wiring scenario I have overlooked, I would like to know what it is.

I don't think it is unreasonable to do something that would be safer 90% of the time just in case your amp encounters the other 10% of cases. It seems to me that normal circumstances are more likely to be than the exceptions, so it makes sense - to me - to protect against what is most likely rather than least likely.

And as Mark suggests, those little outlet checkers with the three lights on them are well worth the ten bucks or whatever. We used to carry those with us on tour to prevent surprises. And that was a long time ago. They still work.

[slowhand401]

Polarity...?

You should always have a grounded cord on your amp. Make sure the hot wire (black) goes first to the fuse then to the switch, with the neutral wire going directly to one side of the transformer primary. Wire the three position switch so that both positions only switch the hot wire. There is no need to switch "polarity" with a grounded cord. The proper way to connect the ground is to have a separate screw in the chassis with nothing else connected to it except the green wire from the line cord. Use a lug that has teeth like a lock washer. I keep #10, #8, and #6 lugs on hand in my shop. You can also dispose of the old capacitor they used on one side of the two conductor line cord. although, if it shorts, the grounded cord will keep the chassis from becoming "hot".

What do you mean by "reverse polarity?"

If the wall outlet is wired wrong, I suppose they could have the hot running to the third prong, and then the chassis would be hot. Unfortunately that leaves ground and neutral for the two power prongs. In that case no two wire device will power up at all, nor will a three wire. If ground and neutral are reversed, then the gear will probably function, but will be noisy - two or three wire.

There are people who smoke three packs a day, those who drive home drunk every night, who do crack at work or while pregnant. And they get away with it. Doesn't mean it is safe or free of risk, it just means they got away with it.

There are miswired outlets to be sure, but to say they seldom are wired right is silly.

If your chassis is grounded, and the amp next to yours is not, and THAT amp gets a hot chassis, then Yes you can get a poke touching both. HAving your amp grounded though prevents IT from being a cause of such situations.


I can think of no reason NOT to make an amp three wired.

Slow, you appear to be new here, and I welcome you. I am not sure why the hostility must be included with some simple disagreement, if that is what we are having. We usually try not to make things into fights here.

I understand reverse polarity certainly, but am not sure exactly what you refer to when you use the term here. Reversed wires in the wall outlet? Reversed wires in some other gear? I am not being a smart ass, I genuinely want to know what you are considering. If there is a wiring scenario I have overlooked, I would like to know what it is.

I don't think it is unreasonable to do something that would be safer 90% of the time just in case your amp encounters the other 10% of cases. It seems to me that normal circumstances are more likely to be than the exceptions, so it makes sense - to me - to protect against what is most likely rather than least likely.

And as Mark suggests, those little outlet checkers with the three lights on them are well worth the ten bucks or whatever. We used to carry those with us on tour to prevent surprises. And that was a long time ago. They still work.

Your'e right, I am new to this site. But that in no way means I am new to
electricity. I been usin' it for 'bout 5o sompin yers now. And for that whole
time, black has been "hot" and white has been "neutral"... If you have those
two wires reversed, THAT is "reverse" polarity.... And just for the record, go
back to where this all begain. Someone ask if they should change the DPDT
switch to a SPDT switch, and all I said was that it was unnessasary and would deprive you (him) of the function of being able to "reverse" the polarity.
I'm not here to get in a pissing match, but when I know I am right, I WILL defend myself. And also for the record, If you have a polarity switch, you don't need no stinkin' "outlet checker".....;-) Randy

[Enzo]

OK. Speaking for myself, there was no attack intended, so no defense needed. Yes, I have been soldering for over 50 years myself - we both have resumes.

Intelligent, experienced people can come to different conclusions.

Are you telling us you prefer ungrounded gear to three wire? Or am I stretching your point too far?

[slowhand401]

evidently you only see what you want to see (disagreement). Absolutely nowhere did I say NOT to use a 3 prong cord. And I actually have no preference one way or the other. They both work fine - just as they should.
But to say, that one more (green) wire is going to cure all the possibilities of
burning your lips on a microphone is a phallisy and maybe even irresponsible...If you tell somebody to add a 3 prong cord and all their troubles will go away is not helping ANYBODY.... And if you have a 3 prong cord you actually NEED a polarity switch. Before there were polarity switches,
we would just go to the wall and turn the plug over (180 degrees) to reverse the polarity, and you can't do THAT with a 3 prong cord, now can you...?

[J Martin]

Sorry if my post seemed critical.

There are industry standards for proper wiring and there is the NEC, (National Electrical Code). Since I operate a repair shop, I adhere to to those standards. I also spent many years as an electrician. Statistical evidence has been compiled since 1897 when the NEC was established as to what constitutes safe practice. The idea being to establish a way of doing things that will be safe in the majority, if not all, situations.

AC has no polarity so a transformer doesn't care how the supply wires attach to the primary. It just so happens that one of those wires is grounded as opposed the the green wire which is used for grounding. There is a difference between grounded and grounding. The cap that people call the "death cap" is just an improvised ground reference. and, btw, that cap is no threat whatsoever if the chassis is grounded. It may blow eventually or you can remove it.

One thing I forgot to mention is that the green grounding wire is supposed to be longer (more slack) than the black and white wires. The idea, according to the code, is that should a situation arise where the cord is accidentally pulled out of an appliance (amp in this case), nothing will be left "hot". If the live wire touches the chassis it will trip your overcurrent device, killing the power.

I own two Gemini amps myself along with a bunch of other Ampegs. Needless to say, they are all properly wired.

[Rob Mercure]

After thinking about it a bit I'm going to weigh in with the majority on this one - like there was any other option - and simply add that any musician without an outlet tester is an idiot! Every outlet not personally wired is suspect (and no circuit breaker is open unless I've opened it - no weapon is unloaded unless I've inspected the breach). And, yes, the "green" wire will protect you from getting your lips shocked if you ensure that the PA and your amp - with a three wire cord - are using the same outlet. Even if the outlet is wired incorrectly both still share the same "ground" and while they may be live to everything else in the universe there is no potential difference.

I'm fairly flexible but there are a few absolutes: I won't play a club or other gig unless I've verified that the power source is properly wired - I've got an "extension" cord made from an old IBM 3000 series power cord - three conductors (should actually be four according to current code) of very flexible 8 ga. wire in a common sheath 30 foot long feeding a 30 amp disconnect/breaker box and then a master outlet. If necessary I tap directly into the the establishment's breaker box. If not, I don't play.

Secondly, unless someone can make a very convincing argument that a "vintage" amp will never be removed from a "collection" and played elsewhere I refuse to service a "two wire" amp unless the owner lets me install a properly grounded three wire cord and lets me move both the fuse and the switch to the live side of the circuit - to date no one has convinced me and no one has refused to replace the two wire cord. Line connected equipment gets an isolation tranny or simply "gets."

I make more money wiring houses than amp repair these days and I won't work on someone's house and leave any unsafe prior wiring that I can identify.

NO ONE GETS ELECTROCUTED ON MY SHIFT! Period! I was raised with too much good old fashioned "catholic guilt" to add anything more and I'd rather lose a job/customer than have even the slightest lingering doubt that my work caused a problem.

Back in my TV service days a fellow worker's repairs to a TV were blamed by an insurance investigator for starting a house fire. Having worked with the fellow I still don't believe it, he really didn't believe it, but the possibility kept him depressed until his death (will be 20 years ago this October - and Jim would have made a hell of a great forum contributor).

So, Slohand401, even if you know you are "correct" are you willing to shoulder the responsibility/guilt should any damage/injury occur that is traced to an amp you've worked on? Now I don't imply in any manner that your work is responsible, I only ask are you so certain that you can't slip up that you are willing to live with the possibility?

"I reserve the right to make a mistake - it's my natural born right and no one can take it away from me."

Rob

[TD_Madden]

This thread fairly crackles with righteous-indignation, so I won't comment on the "correctness" of the parties involved.

I WILL say, though, that I ALWAYS use an outlet tester, and I have ALWAYS replaced the two-conductor cords on my amps with properly configured three-conductor. It's just effective and cheap insurance.

That's my story and I'm sticking to it! :-)